1. Field of the Invention
This invention relates in general to grapples for use in grasping, raking, lifting or moving objects in logging operations, construction, demolition and other industrial fields. In particular, the invention relates to grapples carried on booms which are mounted on equipment such as off-road vehicles and the like.
2. Description of the Related Art
Grapples carried on the booms of wheeled or endless track type tractors are commonly used in logging operations to hoist and move logs or trees. Grapples are also used in a wide variety of construction and demolition activities, such as for moving concrete dividers, rails, large rocks, stumps, trees, chunks of broken concrete or asphalt, debris and other material or objects.
A typical prior art grapple arrangement employs a main boom pivotally mounted on a vehicle, a dipper stick mounted on the end of the main boom and a grapple mounted on the end of the dipper stick. Hydraulic actuators pivot the main boom relative to the vehicle and also pivot the dipper stick relative to the main boom. The typical grapple has two jaws which are pivotally connected to the end of the boom. An hydraulic actuator carried on the dipper stick operates through a linkage to pivot one jaw of the grapple for grasping and releasing objects, such as disclosed in U.S. Pat. Nos. 4,248,471 and 4,907,356. However, the equipment operators of these prior art configurations have a limited degree of control of movement for the grapples. The typical control set-up comprises one lever for raising and lowering the main boom, another lever for controlling pitch of the dipper stick and another lever for controlling pitch of the grapple relative to the dipper stick. In the case where the boom is mounted to the vehicle or structure by a swivel, another lever controls movement of the boom about a vertical axis. After the grapple is holding the load, the operator can only control its pitch attitude by means of the controls for the main boom and dipper stick; there is no independent control for the pitch of the grapple relative to the dipper stick. It would be desirable to provide apparatus in which the grapple can be independently controlled like the wrist joint of the human arm and thereby provide greater versatility in grasping, lifting and moving, and raking ground surface for the clearing of objects.
The prior art also includes grapple configurations in which the grapple is carried through a vertical swivel on the end of a boom or dipper stick, and in which a pair of jaws below the swivel joint are pivoted to open and close by a pair of extensible actuators, such as in U.S. Pat. No. 3,877,743. Configurations of this type also have the drawback of the inability to independently control the pitch of the pair of jaws relative to the boom. In addition, the provision of a single hydraulic actuator for each jaw means that, to provide the requisite thrust forces on the jaws, relatively large moment arms must be provided from the pivot center of the jaws to the thrust line of the actuator. This results in a relatively large change in the length of the moment arm, and therefore a large change in the mechanical advantage, throughout the actuator stroke. It would be desirable to provide a grapple apparatus by which the actuators can apply the requisite thrust forces to the jaws or other tools without an unduly large change in mechanical advantage throughout the stroke.
Quick couple devices have been provided in the prior art for releasably coupling grapples, buckets and the like to the end of booms. These quick couple device employ hooks which are operated to engage sets of pins provided on the grapples or buckets. However, such a quick couple device employs an hydraulic actuator to engage or release a hook with one of the pins, and this entails the use of hydraulic lines into the pressurized fluid circuit as well as a separate control. Such an arrangement increases the complexity and cost of the configuration.
The need has therefore been recognized for a grapple apparatus which obviates the foregoing and other limitations and disadvantages of prior art grapple devices. Despite the various grapple devices in the prior art, there has heretofore not been provided a suitable and attractive solution to these problems.